Updating magnetic resonance imaging of small bowel: Imaging protocols and clinical indications

Manganese-free chow, a refined non-invasive solution to reduce gastrointestinal signal for T1-weighted magnetic resonance imaging of the mouse abdomen

Commercial mouse chow is designed to provide a complete, nutrient-rich diet, and it can contain upwards of 100 mg/kg manganese, an essential mineral. Manganese acts as a relaxation time-shortening contrast agent for both T1 and T2, and where standard chow is hydrated in the gastrointestinal tract, bright signals are produced when using T1-weighted imaging (T1WI). As a result of peristalsis, gastrointestinal hyperintensities result in temporally unstable signals, leading to image ghosting and decreased resolution from that prescribed. To avoid the problem, various methods of gastrointestinal tract modulation, including the use of intestinal cleansing with laxatives and dietary modulation, have been reported. Here, dietary modulation has been extended to the use of a biologically innocuous, long-term change of diet. In this study, we report on the use of a commercially available manganese-free chow to improve the image quality of the gastrointestinal tract. This manganese-free chow, apart from the omitted manganese which is available in tap water, is a complete diet and readily available. We investigated the time-dependent, diet-related gastrointestinal intensities on short-TR T1WI magnetic resonance imaging; monitored body mass, food and water consumption and standard blood biochemistry analysis following diet change; and determined manganese concentration in blood plasma following a five-day change to manganese-free chow. We show that the manganese-free chow presents a refinement to other gastrointestinal tract modulation, as it avoids the need for invasive procedures for gut voiding and can be provided ad libitum so that animals can be maintained with no need for prescribed diet change before imaging.

Nanoparticles of gadolinium-incorporated Prussian blue with PEG coating as an effective oral MRI contrast agent for gastrointestinal tract imaging

Biocompatible nanoparticles of gadolinium-incorporated Prussian blue with the empirical formula K(0.94)Gd(0.02)Fe[Fe(CN)6] exhibit extremely high stability against the release of Gd(3+) and CN(-) ions under the acidic conditions similar to stomach juice. The high r1 relaxivity, low cytotoxicity and the ability of such nanoparticles to penetrate the cell membrane suggest that this coordination-polymer structural platform offers a unique opportunity for developing the next generation of T1-weighted oral cellular MRI probes for the early detection of tumors in the gastrointestinal tract.

Current tecniques and new perpectives research of magnetic resonance enterography in pediatric Crohn's disease

Crohn's disease affects more than 500000 individuals in the United States, and about 25% of cases are diagnosed during the pediatric period. Imaging of the bowel has undergone dramatic changes in the past two decades. The endoscopy with biopsy is generally considered the diagnostic reference standard, this combination can evaluates only the mucosa, not inflammation or fibrosis in the mucosa. Actually, the only modalities that can visualize submucosal tissues throughout the small bowel are the computed tomography (CT) enterography (CTE) with the magnetic resonance enterography (MRE). CT generally is highly utilized, but there is growing concern over ionizing radiation and cancer risk; it is a very important aspect to keep in consideration in pediatric patients. In contrast to CTE, MRE does not subject patients to ionizing radiation and can be used to detect detailed morphologic information and functional data of bowel disease, to monitor the effects of medical therapy more accurately, to detect residual active disease even in patients showing apparent clinical resolution and to guide treatment more accurately.

Small Bowel Imaging: Clinical Applications of the Different Imaging Modalities—A Comprehensive Review

In the last years, MR and CT techniques have been optimized for small bowel imaging and are playing an increasing role in the evaluation of small bowel disorders. In comparison to traditional barium fluoroscopic examinations, spatial and temporal resolution is now much more improved partially thanks to modern bowel distending agents. However, there is a global interest in implementing techniques that either reduce or eliminate radiation exposure. This is especially important in patients with chronic diseases such as inflammatory bowel disease who may require multiple studies over a lifetime. Owing to the excellent soft tissue contrast, direct multiplanar imaging capabilities, new ultrafast breath-holding pulse sequences, lack of ionizing radiation, and availability of a variety of oral contrast agents, MR is well suited to play a critical role in the imaging of small bowel disorders.

Parenchymal signal intensity in 3-T body MRI of dogs with hematopoietic neoplasia

We performed a preliminary study involving 10 dogs to assess the applicability of body MRI for staging of canine diffuse hematopoietic neoplasia. T1-weighted (before and after intravenous gadolinium), T2-weighted, in-phase, out-of-phase, and short tau inversion recovery pulse sequences were used. By using digital region of interest (ROI) and visual comparison techniques, relative parenchymal organ (medial iliac lymph nodes, liver, spleen, kidney cortex, and kidney medulla) signal intensity was quantified as less than, equal to, or greater than that of skeletal muscle in 2 clinically normal young adult dogs and 10 dogs affected with either B-cell lymphoma (n = 7) or myelodysplastic syndrome (n = 3). Falciform fat and urinary bladder were evaluated to provide additional perspective regarding signal intensity from the pulse sequences. Dogs with nonfocal disease could be distinguished from normal dogs according to both the visual and ROI signal-intensity relationships. In normal dogs, liver signal intensity on the T2-weighted sequence was greater than that of skeletal muscle by using either the visual or ROI approach. However in affected dogs, T2-weighted liver signal intensity was less than that of skeletal muscle by using either the ROI approach (10 of 10 dogs) or the visual approach (9 of 10 dogs). These findings suggest that the comparison of relative signal intensity among organs may have merit as a research model for infiltrative parenchymal disease (ROI approach) or metabolic effects of disease; this comparison may have practical clinical applicability (visual comparison approach) as well.

MR imaging of the small bowel

Small-bowel radiology has undergone dramatic changes in the past 2 decades. Despite important recent advances in small-bowel endoscopy, radiologic imaging remains important for patients suspected of having or with established small-bowel disease. Cross-sectional imaging techniques (computed tomography and magnetic resonance [MR] imaging), used to investigate both extraluminal abnormalities and intraluminal changes, have gradually replaced barium contrast examinations, which are, however, still used to examine early mucosal disease. MR imaging techniques clearly highlight endoluminal, mural and extramural enteric details and provide vascular and functional information, thereby enhancing the diagnostic value of these techniques in small-bowel diseases. Two MR imaging based techniques are currently utilized: MR enteroclysis and MR enterography. In enteroclysis, enteric contrast material is administered through a nasoenteric tube, whereas in enterography, large volumes of enteric contrast material are administered orally. MR enteroclysis ensures consistently better luminal distention than does MR enterography in both the jejunum and the ileum and more accurately depicts endoluminal abnormalities and early disease, particularly at the level of the jejunal loops. Moreover, MR enteroclysis provides a high level of accuracy in the diagnosis and exclusion of small-bowel inflammatory and neoplastic diseases and can be used for the first radiologic evaluation, while MR enterography may effectively be used to follow up both Crohn disease patients without jejunal disease and in pediatric patients where nasogastric intubation might be a problem. MR enteroclysis may also reveal subtle transition points or an obstruction in the lower small bowel, which may escape detection when more routine methods, including enterography, are used. MR imaging offers detailed morphologic information and functional data of small-bowel diseases and provides reliable evidence of normalcy, thereby allowing the diagnosis of early or subtle structural abnormalities and guiding treatment and decisions in patient care.

[MRI enterography in the assessment of paediatric Crohn's disease]

OBJECTIVE

To determine the usefulness of MRI enterography for assessing the extension and activity of paediatric Crohn's disease. MRI findings were compared with clinical, biological, endoscopic and other imaging data.

PATIENTS AND METHODS

Studies of MRI enterography use in patients younger than 18 years of age were reviewed. Patients received 500-1000mL of polyethylene glycol one hour before examination (1.5-TMR). T2 HASTE sequences with or without fat saturation, T2 true-FISP, T1 with fat saturation, pre- and post gadolinium-enhanced VIBE sequences, and dynamic and diffusion HASTE were acquired. Thickening of the bowel wall, mucosal enhancement, and extra-luminal complications were evaluated. Five MRI patterns (normal, fibrosis, mild, moderate, and severe transmural activity) were defined. Findings were compared with PCDAI scores, inflammatory parameters, and endoscopic and histological results.

RESULTS

Twenty-two studies were reviewed. Optimal intestinal distension was present in 82% of the cases. Mild side effects were observed in 12% of patients. There was a significant relationship between MRI patterns and PCDAI scores (P=.002), sedimentation rate (P=.006) and serum PCR levels (P=.047) and a non-significant relationship with the histology (P=.571). MRI enterography correctly assessed the ileal (80%) and colonic (66%) extension. Extra-luminal complications unrelated to MRI classification (P=.274) were reported in 86.4% of studies.

CONCLUSIONS

There was a significant relationship between MRI patterns and PCR, sedimentation rate, and PCDAI scores. MRI enterography showed excellent agreement with ileoscopies, and allowed endoscopically non-accessible areas to be assessed, as well as the diagnosis of extra-luminal complications without irradiation.

Crohn's disease imaging: a review

Crohn's disease is a chronic granulomatous inflammatory disease of the gastrointestinal tract, which can involve almost any segment from the mouth to the anus. Typically, Crohn's lesions attain segmental and asynchronous distribution with varying levels of seriousness, although the sites most frequently involved are the terminal ileum and the proximal colon. A single gold standard for the diagnosis of CD is not available and the diagnosis of CD is confirmed by clinical evaluation and a combination of endoscopic, histological, radiological, and/or biochemical investigations. In recent years, many studies have been performed to investigate the diagnostic potential of less invasive and more patient-friendly imaging modalities in the evaluation of Crohn's disease including conventional enteroclysis, ultrasonography, color-power Doppler, contrast-enhanced ultrasonography, multidetector CT enteroclysis, MRI enteroclysis, and 99mTc-HMPAO-labeled leukocyte scintigraphy. The potential diagnostic role of each imaging modality has to be considered in different clinical degrees of the disease, because there is no single imaging technique that allows a correct diagnosis and may be performed with similar results in every institution. The aim of this paper is to point out the advantages and limitations of the various imaging techniques in patients with suspected or proven Crohn's disease.

Malignant tumours of the small intestine: a review of histopathology, multidetector CT and MRI aspects

Small bowel neoplasms, including adenocarcinoma, carcinoid tumour, lymphoma and gastrointestinal stromal tumours, represent a small percentage of gastrointestinal cancers, yet are among those with the poorest prognosis compared with other gastrointestinal malignancies. Unclear clinical scenarios and difficult radiological diagnosis often delay treatment with negative effects on patient survival. Recently, multidetector CT (MDCT) and MRI have been introduced as feasible and accurate diagnostic techniques for the identification and staging of small bowel neoplasms. These techniques are gradually replacing conventional barium radiography as the tool of choice. However, the inherent technical and physiological challenges of small bowel imaging require a familiarity with patient preparation and scan protocols. Adequate knowledge of the histopathology and natural evolution of small bowel neoplasms is also important for differential diagnosis. The aim of this article is to review MDCT and MRI protocols for the evaluation of small bowel tumours and to provide a concise yet comprehensive guide to the most relevant imaging features relative to histopathology.

Imaging of malignant neoplasms of the mesenteric small bowel: new trends and perspectives

This article describes the recent advances in radiological imaging of malignant neoplasms of the mesenteric small bowel and provides an outline of new trends and perspectives that can be anticipated. The introduction of multidetector row technology, which allows the acquisition of submillimeter and isotropic voxels, has dramatically improved the capabilities of computed tomography in the investigation of the mesenteric small bowel. This technology combined with optimal filling of small bowel loops through the use of appropriate enteral contrast agents has markedly changed small bowel imaging. Computed tomography-enteroclysis, which is based on direct infusion of enteral contrast agent into the mesenteric small bowel through a naso-jejunal tube, provides optimal luminal distension. By contrast, computed tomography-enterography is based on oral administration of enteral contrast agent. These two techniques are now well-established ones for the detection and the characterization of small bowel neoplasms. During the same time, combining the advantages of unsurpassed soft tissue contrast and lack of ionizing radiation, magnetic resonance imaging has gained wide acceptance for the evaluation of patients with suspected small bowel neoplasms. Rapid magnetic resonance imaging sequences used in combination with specific enteral contrast agents generate superb images of the mesenteric small bowel so that magnetic resonance-enteroclysis and magnetic resonance-enterography are now considered as effective diagnostic tools for both the detection and the characterization of neoplasms of the mesenteric small bowel. Recent improvements in image post-processing capabilities help obtain realistic three-dimensional representations of tumors and virtual enteroscopic views of the small bowel that are useful for the surgeon and the gastroenteroenteologist to plan surgical or endoscopic interventions. Along with a better knowledge of the potential and limitations of wireless capsule endoscopy and new endoscopic techniques, these recent developments in radiological imaging reasonably suggest that substantial changes in the investigation of small bowel tumors may be anticipated in a near future, thus potentially create a new paradigm shift after standard small bowel follow-through study has been universally abandoned.

The role of nasoenteric intubation in the MR study of patients with Crohn's disease: our experience and literature review

PURPOSE

The aim of this study was to compare magnetic resonance (MR) enteroclysis with MR enterography to verify whether nasoenteric intubation in patients affected by Crohn's disease can provide supplementary information to that afforded by MR study of the small bowel.

MATERIALS AND METHODS

In a 12-month period, 40 patients (28 women and 12 men, mean age 35 years) affected by Crohn's disease underwent MR imaging. Distension of the small-bowel loops was obtained by administering polyethylene glycol: 15 patients were given the mixture by mouth (MR enterography), whereas the remaining 25 received it via nasoenteric intubation (MR enteroclysis). Our study protocol included morphological sequences taken before and after intravenous injection of contrast medium and real-time functional sequences. Accuracy criteria for the execution of the examinations were designed according to 11 bands.

RESULTS

Complete distension of the small-bowel loops was obtained in the 25 patients who underwent MR enteroclysis, with the additional advantage of a suitable assessment of those segments involved in the pathological process. This was not the case for the 15 patients who underwent MR enterography, because both the jejunum and the small-bowel loops appeared partially collapsed.

CONCLUSIONS

MR enteroclysis is the most effective technique for studying the small bowel in Crohn's disease, as it not only provides a suitable morphological assessment but also supplies functional information.

MRI for diagnosis and evaluation of inflammatory bowel disease

As a non-invasive and ionizing radiation-free cross-sectional imaging technique, magnetic resonance imaging (MRI) has shown a bright future in following up patients with inflammatory bowel disease (IBD), especially child and young adult patients. The application of new techniques in MRI makes it possible to obtain MRI images that are richer in information and to evaluate the activity of IBD more objectively and quantitatively. This improvement is of great significance for clinical decision-making and evaluation of drug efficacy in IBD patients.

Magnetic resonance follow-through imaging for evaluation of disease activity in ileal Crohn's disease: an observational, retrospective cohort study

BACKGROUND

Magnetic resonance follow-through (MRFT) is a new cross-sectional imaging modality with the potential to accurately stage ileal Crohn's disease (CD), while avoiding ionizing radiation and the discomfort associated with enteroclysis. We aimed to assess the reliability of this technique in assessing the extent and activity of ileal CD, and to assess its influence on subsequent management.

METHODS

Out of a total of 342 patients undergoing MRFT between 2004 and 2008, 221 were performed in 191 patients with confirmed CD. Case notes were reviewed in detail with documentation of all investigations pre- and post-MRFT. Agreement between inflammatory markers, histopathology, and MRFT findings was determined.

RESULTS

Overall, 116/221 (52.5%) of MRFTs showed active ileal CD, and 76/221 (34.4%) quiescent CD, while 29/221 (13.1%) were suboptimal. Overall, 66 strictures and 18 fistulae were identified. There was substantial agreement between active ileal CD on MRFT and histopathology (n = 59; kappa = 0.66; P = 0.0006; sensitivity 85.1%, specificity 85.7%) and fecal calprotectin (n = 14; kappa = 0.72; P = 0.047), while C-reactive protein (CRP) showed moderate agreement (n = 107; kappa = 0.402; P = 0.00028). Management was influenced by MRFT reports following active (52/84, 62% treated medically) or quiescent (48/62, 77.4% managed conservatively) disease. Fibrotic strictures were predominantly treated surgically (7/14, 50%). In all, 13/32 (40.6%) patients with inflammatory ileal strictures required surgery, mostly due to steroid-resistant disease. Overall, 75 MR findings were documented in 221 MRFTs, including 1 renal cancer.

CONCLUSIONS

MRFT provides accurate information on ileal CD activity, with close agreement to inflammatory markers and histopathology. It represents a substantial advance in the staging of CD, while avoiding painful enteroclysis and radiation exposure in young patients.

Benefits and challenges in bowel MR imaging at 3.0 T

Abdominal imaging at 3.0 T has shown to be challenging because of a number of artifacts and effects related to the physics at higher field strength. For bowel imaging at 3.0 T, artifacts due to magnetic field inhomogeneities, standing waves, increased susceptibility, and greater chemical shift effects are of particular concern because they are likely to affect the assessment of relevant structures and counterbalance the benefits of higher signal-to-noise ratio. Regarding small- and large-bowel magnetic resonance imaging, the benefits of higher field strengths translate mainly in better contrast-to-noise ratio of contrast-enhanced T1-weighted gradient echo and T2-weighted imaging, whereas steady-state free precession sequences seem to suffer from serious degradation of image quality. The present article summarizes the technical challenges in bowel imaging at 3.0 T, provides an overview of performance compared with 1.5 T in small- and large-bowel diseases including the rectum, and revises the current literature.

[Diarrhea, from the gastroenterologist's point of view]

Patients seeking help from gastroenterologist have frequent complaints of changes in the quality and quantity of stool as well in the frequency of bowel movements. Definition of diarrhea includes: more than three bowel movements daily, more than 200 grams of the stool daily, and its water content exceeding 75-85%. Diarrhea lowers the quality of life and can be a sign of organic disease. Its course can be acute and chronic. According to the pathomechanism, diarrheas can be divided into four different types: exudative (inflammatory), osmotic, dismotility and secretory. Acute diarrheas are usually infective, and sometimes they result in very serious conditions. Their course runs from a few days to a couple of weeks. If diarrhea persists more than four weeks, it is the chronic variant and it justifies gastroenterological examination. During the evaluation, we have to think of endocrine, autoimmune, allergic, postoperative states and the side effect of medications beside primer gastroenterological causes. To differentiate from a number of wide scale of clinical pictures and to reach the correct diagnosis, we are aided by the characteristics of diarrhea, the accompanying symptoms, laboratory values and invasive examinations. With the present summary, we would like to give a guide to the practicing physicians, mainly with a symptom-oriented approach.